Introduction 1 10 11 12 This article gives a brief overview of the central venous access devices available and the potential causes of catheter malfunction. A standard catheter contrast study or ‘linogram’ technique is described. The normal appearances of such a study and a detailed pictorial review of abnormal catheter studies are provided, together with a brief overview of how information from catheter investigations can guide the management of catheter complications. Background Central venous access is required for the safe delivery of a number of drugs and other intravenous therapies into large-calibre vessels, to allow adequate dilution of the drug and avoid vessel irritation. Here the term ‘central’ is taken to encompass the brachiocephalic veins, the superior vena cava (SVC), the suprahepatic inferior vena cava (IVC) and the right atrium (RA). A centrally placed catheter with a reasonable-size lumen also allows regular noninvasive blood sampling, which has significant benefits for both the clinical team and the patient. 13 20 8 21 25 26 27 8 22 28 30 Catheter types 1 2 Fig. 1 Inset  Fig. 2 A permanent (tunnelled) haemodialysis catheter with staggered tip for optimal flow rates (12.5F Vas-Cath Soft Cell; Bard Access Systems, Salt Lake City, Utah)  3 Fig. 3 Inset  4 5 Fig. 4 A triple-lumen 7F catheter (Arrow-Howes; Arrow International, Reading, Pa.) for short-term nontunnelled central venous access  Fig. 5 A double-lumen 5F PICC (Bard Access Systems, Salt Lake City, Utah)  Strategies in managing catheter malfunction 3 10 31 Initial examination of the catheter It is important to examine both the catheter and its skin exit site prior to performing any radiographic investigation, so that a simple cause of catheter malfunction, such as a break in the catheter itself or wear at the clamp site, can be established. It is not uncommon to find that the skin suture of a newly placed catheter is too tight and is restricting flow. Fluoroscopic or plain radiographic views 6 7 8 9 10 11 12 Fig. 6 a b  Fig. 7 A chest radiograph in a 13-month-old male with a permanent haemodialysis catheter, the tip of which lies at or beyond the level of the tricuspid valve causing intermittently poor flow rates  Fig. 8 a arrow b  Fig. 9 arrow  Fig. 10 a b a b  Fig. 11 Chest radiograph of a 9-month-old infant with a tunnelled CVC in situ. The catheter has migrated back into the redundant soft tissues of the neck and chest wall  Fig. 12 a short arrow long arrow b  Performing a contrast study If the initial examination of the line is unremarkable, a contrast-enhanced study (‘linogram’) should be performed. The catheter should be accessed using a sterile technique and, where possible, any heparin solution dwelling in the line should be aspirated and discarded. Inability to aspirate from the catheter should be documented, as this narrows the list of potential causes of catheter malfunction, as discussed below. If only one lumen of a multilumen catheter is malfunctioning, imaging should first be performed through the functioning lumen as this may demonstrate the underlying problem and obviate the need for access of the second lumen. Water-soluble nonionic contrast medium should be used and the operator should aim to minimize the dose of contrast medium that the child receives. 13 14 Fig. 13 Fluoroscopic imaging of a tunnelled catheter in a 4-month-old female. The entire catheter is imaged during slow instillation of contrast medium  Fig. 14 a b a b  15 16 Fig. 15 Fluoroscopic image of contrast medium flowing freely from the catheter tip in an 8-year-old male. The contrast medium immediately fans out to fill the right atrium  Fig. 16 Normal appearance of the contrast medium jet exiting the side hole of a PICC  It is important to remember to study both lumens of a double-lumen catheter if injection of the first lumen is normal. In patients with intermittent catheter malfunction, attempts should be made to recreate the situation in which problems occur; often, catheter function is position-dependent and placing the child in the troublesome position may demonstrate the cause of catheter malfunction. This may include a significant change in tip position following a change in posture or intermittent occlusion of the catheter lumen at the level of the clavicle due to catheter compression between the clavicle and the first rib (‘pinch-off’ syndrome). If the child presents with symptoms of venous occlusion, such as localized pain and swelling over the venous access site or sudden swelling of the face or extremity, a formal venogram via a peripheral cannula can be performed to determine the presence of catheter-related venous thrombosis (see below). Once the study is completed, the catheter should always be flushed and, where required, ‘locked’ with heparin solution of an appropriate concentration. This should be documented in the clinical notes as part of the examination. If the catheter is deemed unsafe for use, this too should be clearly documented. Interpreting an abnormal contrast study 17 18 Fig. 17 a arrows b arrow  Fig. 18 a b  19 Fig. 19 a b  20 Fig. 20 Fluoroscopic contrast study of a haemodialysis catheter in a 9-year-old female. The lumen with a more distal tip has been opacified. The catheter is too long and the distal tip lies up against the inferior wall of the right atrium, causing the contrast jet to be deflected  8 32 33 21 22 Fig. 21 a b a arrow b c  Fig. 22 a arrow b arrow c 21  21 23 24 25 Fig. 23 arrow  Fig. 24 a b  Fig. 25 long white arrows black arrows  34 38 39 34 25 26 27 Fig. 26 Left arm venography in a 1-year-old female with a malfunctioning tunnelled catheter in situ. Contrast medium fails to fill the occluded SVC and there are irregular filling defects within the left brachiocephalic vein, consistent with mural thrombi. Small collaterals are forming in the left supraclavicular region  Fig. 27 Right arm venogram in an 8-year-old boy performed prior to placement of a new catheter. The study demonstrates multiple irregular venous collaterals draining the arm following occlusion of the subclavian and brachiocephalic veins  Implications for catheter salvage techniques 10 40 45 46 47 Kinks in the subcutaneous tunnel of a CVC can often be straightened by accessing either the venous access site or the skin exit site of the catheter. Intervention at the venous access site may result in an increase in the intravascular length of the catheter, a result that is beneficial in catheters that have migrated back into the tunnel or the neck. 10 10 48 10 49 51 9 10 28 9 10 51 55 32 55 Fig. 28 The distal portion of a malfunctioning haemodialysis catheter has been snared from a femoral approach in an attempt to strip the fibrin sheath from the catheter  Implications for catheter replacement techniques 29 9 53 Fig. 29 arrow  Documentation of complete venous occlusion is vital prior to replacement of a CVC. This allows a more considered approach to catheter placement and appropriate discussion with the family prior to a difficult procedure. Recanalization and venous stenting techniques or use of unusual access sites should be considered in children who would otherwise require open surgical procedures to maintain reliable venous access. Conclusion Reliable central venous access is key to the management of many paediatric conditions. The insertion of central venous access devices is increasingly becoming the remit of the interventional radiologist, a paradigm shift that will require general radiologists to play some role in the subsequent management of these catheters. In institutions where the specific cause of catheter malfunction may alter subsequent management, radiologists need to be familiar with the catheter types used and their imaging appearances, both on plain radiography and on contrast investigations. Accurate diagnosis of CVC malfunction can significantly alter outcome for patients in whom repeated venous access procedures can often become a source of greater morbidity than their primary condition.